<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        span {
            color: red;
        }
        #one {
            color: aqua;
        }
        .duo {
            color: blue;
            font-size: 30px;
        }
    </style>
</head>
<body>
    <span>加油
    </span>
    <!-- id选择器只能命名一个 -->
    <p id="one">这是id选择器</p>
    <!-- 类选择器可以命名一个或多个 -->
    <h5 class="duo">这是类选择器</h5>
    <h6 class="duo">类选择器可以有多个</h6>
</body>
</html>